Due to actualization of environmental problems of recent years, development of hybrid cars and electric cars has been activated and spread thereof has been promoted. In each of such vehicles, waste heat of an engine which has heretofore been used for air condition in the vehicle cannot sufficiently be utilized. Therefore, a heating device using an electric heating wire heater as a heating element is mounted in the vehicle, and the heating device is used as an auxiliary heat source to compensate for the waste heat of the engine in the hybrid car, or used as a substitute heat source in place of the engine in the electric car, to heat a heat medium such as cooling water which flows through a circuit of an air conditioning device for the vehicle (e.g., see Patent Document 1).
In such a heating device, a flow path through which the heat medium flows is constituted in a case, and the heating element is disposed in this flow path to heat the heat medium. Therefore, heat exchange between the heating element and the heat medium has to be activated to improve a heating performance.
To solve the problem, in Patent Document 1 described above, the heating device is contrived so that a guide is formed in an outer surface of a first case body in which the heating element is received, and the flow of the heat medium in the flow path is turned by this partition wall, to lengthen a period of time when the heat exchange between the heating element, and the heat medium is performed via the first case body. In addition, it has been suggested that a meandering cooling water passage is formed in a casing, a heater is disposed in this passage in a meandering manner, and further on a wall of the cooling water passage, a plurality of convex portions are alternately formed to impose restrictions on flow of a heat medium, whereby heat exchange between the heat medium and the heater is performed (e.g., see Patent Document 2),